1. Field of the Invention
The present invention relates to an optical isolator with an optical fiber used for optical communication, optical information processing, optical measurement and so forth.
2. Related Art
Optical isolators are used for optical amplifiers, semiconductor laser units and so forth.
These optical isolators comprise two of polarizers fixed to each other with a relative angle of about 45xc2x0 via a Faraday rotator inserted between them, which has a Faraday rotation angle of about 45xc2x0. They have an effect for passing through light of the forward direction but shielding light of the reverse direction.
Recently, smaller size, large scale production and lower cost of these optical isolators are strongly desired, and optical isolators with an optical fiber, in which an optical isolator and an optical fiber are integrated, have been proposed as a measure for answering the aforementioned demands. For example, in the optical isolator disclosed in Japanese Patent Laid-open Publication No. 6-88926, it is attempted to directly attach an optical isolator to a ferrule-processed end of an optical fiber. There is disclosed a method of assembling an isolator by utilizing a shape protruding from a ferrule, which is composed of glass tube or ceramics such as those of Zr, in order to secure bonding strength of the parts. However, with the shape disclosed therein, positional fixation of an optical element (it consists of a polarizer and a Faraday rotator, and it is also called an isolator element) is quite difficult. The facilitation of the positional fixation depends on the dimensional accuracy of the internal diameter of magnet and the outer diameter of the optical element, and it eventually depends on the outer peripheral shape of the glass tube part. Therefore, the degree of freedom concerning the shape of the optical element will eventually be lost.
Further, in an example disclosed in Japanese Patent Laid-open Publication No. 9-325299, it is necessary to additionally use a metal member having a level difference for fixing the element around the ferrule in order to integrate the optical isolator element, a permanent magnet and an optical fiber held by the ferrule. Therefore, it suffers from a drawback that it cannot use general-purpose parts, and therefore the cost becomes high.
Therefore, the present invention was accomplished in view of the aforementioned problems, and its object is to provide a reliable and low cost ferrule connection type optical isolator with the optical fiber that can connect and integrate an optical isolator element, a permanent magnet and an optical fiber held by a ferrule by using only general-purpose parts that neither have a special shape nor are subjected to a special processing and can realize positional adjustment in assembly with high precision while securing the degree of freedom for the shape of optical element.
In order to achieve the aforementioned object, the present invention provides a ferrule connection type optical isolator with an optical fiber, wherein the optical isolator comprises a ferrule in which at least one processed end surface of an optical fiber consists of two kinds of materials and which has a concentric level difference between the different kinds of materials, a small cylindrical magnet having a size larger than the outer diameter of the level difference portion but smaller than the outermost diameter of the ferrule is connected to the level difference portion, a guide ring is inserted and fixed in the magnet, and an optical element that consists of at least one polarizer and at least one Faraday rotator is connected and fixed in the guide ring.
Since the optical isolator of the present invention uses two kinds of constitutional materials for the ferrule, and connects and fixes the optical isolator element and the optical fiber by utilizing the level difference of the constitutional members as described above, it can be a reliable and low cost ferrule connection type optical isolator with the optical fiber that can connect and integrate an optical isolator element, a permanent magnet and an optical fiber held by a ferrule by using only general-purpose parts that neither have a special shape nor are subjected to a special processing and is undergone positional adjustment in assembly with high precision while securing the degree of freedom for the shape of optical element.
In the above optical isolator, an end portion of the guide ring on the ferrule side may be made perpendicular to the length direction of the guide ring, and the guide ring in which the optical element is connected and fixed beforehand may be inserted into the cylindrical magnet to adjust its position so as to conform to the shape of the protrusion of the ferrule end for positional adjustment with respect to the ferrule end.
This structure enables easy and highly precise positional adjustment in assembly, and thus cost reduction can be contemplated.
Further, in the above optical isolator, the element center position of the Faraday rotator to be connected and fixed is preferably located outside the magnetic field center of the magnet disposed on outer periphery of the optical element viewing from the end of the ferrule.
Such a structure enables easy insertion and fixation of the optical element in the guide ring thanks to the magnetic field of the magnet, and it can also prevent variation of the connecting position of the optical element.
Furthermore, in the above optical isolator, the guide ring preferably consists of a magnetic substance, and the center position of the guide ring is preferably located outside the magnetic field center of the magnet viewing from the end of the ferrule.
Such a structure enables easy insertion and fixation of the optical element, which is located and fixed in the guide ring beforehand, in the magnet together with the guide ring thanks to the magnetic field of the magnet.
Furthermore, the present invention also provides a ferrule connection type optical isolator with an optical fiber, wherein the optical isolator comprises a ferrule in which at least one processed end surface of an optical fiber consists of two kinds of materials and which has a concentric level difference between the different kinds of materials, a guide panel having a processed end of a size larger than the outer diameter of the level difference portion but smaller than the outermost diameter of the ferrule on the ferrule side is disposed on the level difference portion, which guide panel is positioned by the ferrule level difference when it is connected and fixed and serves as means for compensating the level difference, a magnet is connected and fixed on a side of the guide panel opposite to the side on which the ferrule is connected, the magnet has a cylindrical pocket having an inner diameter larger than the outermost diameter of the optical element or square prismatic pocket or inserting the optical element, and the optical element is fixed in the magnet.
The optical isolator of the structure described above also can be a reliable and low cost ferrule connection type optical isolator with the optical fiber that can connect and integrate an optical isolator element, a permanent magnet and an optical fiber held by a ferrule by using only general-purpose parts that neither have a special shape nor are subjected to a special processing and is undergone positional adjustment in assembly with high precision while securing the degree of freedom for the shape of optical element.
In the above optical isolator, the guide panel can be one having a shape with a level difference portion having a size smaller than the outermost diameter of the ferrule and larger than the outer diameter of the magnet on the side opposite to the side connected to the ferrule, the magnet can be fixed on the level difference portion, the magnet has a cylindrical pocket having an inner diameter larger than the outermost diameter of the optical element or square prismatic pocket for inserting the optical element, and the optical element is fixed in the magnet.
Since the aforementioned structure of the guide panel utilizes the level difference of the ferrule, the magnet accommodating the optical element and the ferrule can easily be connected and integrated, and the positional adjustment of the optical element can easily be performed.
Furthermore, the present invention also provides a ferrule connection type optical isolator with an optical fiber, wherein the optical isolator comprises a ferrule in which at least one processed end surface of an optical fiber consists of two kinds of materials and which has a concentric level difference between the different kinds of materials, a magnet having a shoulder with two inner diameters including a first inner diameter larger than the outer diameter of the level difference portion and smaller than the outermost diameter of ferrule and a second inner diameter larger than the outer diameter of an optical element to be inserted is fitted and fixed on the level difference portion, and an optical element that comprises at least one polarizer and at least one Faraday rotator is connected and fixed in a portion having the second diameter.
The optical isolator of the structure described above also can be a reliable and low cost ferrule connection type optical isolator with the optical fiber that can connect and integrate an optical isolator element, a permanent magnet and an optical fiber held by a ferrule by using only general-purpose parts that neither have a special shape nor are subjected to a special processing and is undergone positional adjustment in assembly with high precision while securing the degree of freedom for the shape of optical element. This structure does not require the guide ring.
In addition, the present invention also provides a ferrule connection type optical isolator with an optical fiber, wherein the optical isolator comprises a ferrule in which at least one processed end surface of an optical fiber consists of two kinds of materials and which has a concentric level difference between the different kinds of materials, a part having a shoulder with two inner diameters including a first inner diameter larger than the outer diameter of the level difference portion and smaller than the outermost diameter of ferrule and a second inner diameter larger than the outer diameter of an optical element to be inserted is fitted and fixed on the level difference portion, and an optical element that comprises at least one polarizer and at least one latching type Faraday rotator is connected and fixed in a portion of the part having the second diameter.
If the Faraday rotator is of a latching type as described above, the aforementioned permanent magnet having the two of inner diameters (having a level difference) can be replaced with a part of the same shape made of a material other than magnet such as a metal part, and an effect comparable to that obtained by the magnet can be obtained with such a part.
The present invention also provides a ferrule connection type optical isolator with an optical fiber, wherein the optical isolator comprises a ferrule in which at least one processed end surface of an optical fiber consists of two kinds of materials and which has a concentric level difference between the different kinds of materials, an optical element having an outermost diameter smaller than the outer diameter of the level difference portion is positioned with respect to the ferrule and fixed on the level difference portion by using a jig, and thereafter a magnet having an inner diameter larger than the outer diameter of the level difference portion is connected and fixed to the level difference portion by utilizing the level difference.
As described above, the optical element may be positioned and fixed beforehand at the center of the ferrule by using a jig of the same shape as the aforementioned magnet, and then a cylindrical magnet may be connected and fixed. As for the jig for positioning the optical element used here, a part to be in contact with the optical element preferably has a shape processed into a round shape or a square shape conforming to the shape of the optical element.
In any of the aforementioned ferrule connection type optical isolators with an optical fiber, it is preferred that a surface of the optical element most close to the ferrule is directly connected and fixed to the ferrule.
Such a structure can provide sufficiently high reliability of the connected portion, even if the end surface of the optical fiber on the ferrule end is very small.
Further, in any of the aforementioned ferrule connection type optical isolators with an optical fiber, it is preferred that connection and fixation of parts including those of the optical element to the ferrule end are attained by using an adhesive on curing condition of 100xc2x0 C. or lower, and a silicone resin type adhesive is suitable for the adhesive.
Silicone resin type adhesives show superior adhesion strength even at a curing temperature of 100xc2x0 C. or lower, excellent weather resistance such as moisture resistance, heat resistance and laser damage threshold, and high light transmittance. Therefore, they are most suitable adhesives for use in light-transmitting surface.
If the connection and fixation temperature becomes high exceeding 100xc2x0 C., the optical fiber may protrude or retract from the processed surface of the optical fiber. Therefore, the connection and fixation temperature is preferably 100xc2x0 C. or lower.
When the aforementioned guide panel or the part having a shoulder is made of a metal, it is desirable that such a metal part should be fixed by YAG welding.
If the metal part is fixed by YAG welding, i.e., minute spot-welding method by yttrium-aluminium-garnet laser beam, it can be easily welded and fixed without thermally damaging the optical element and adversely affecting the assembly precision.
According to the present invention, the degree of freedom in the design of components for the optical element can be increased by enabling use of general-purpose processed products for optical fiber ferrules, without requiring special shapes or processing, to simplify the shapes of constitutional members for optical isolators. Thus, there can be provided a highly reliable and highly precise ferrule connection type optical isolator with an optical fiber that can realize easy positioning of parts in assembly at a low cost and firm connection and fixation.